If you cannot access Google Drive assignments or files in Schoology, you may need to remove / revoke Schoology access to your Google Drive and then re-add it.
How to Revoke Schoology App Access
In your Chrome browser, click your avatar and select Manage your Google account OR click the Google Apps waffle icon and select Account.
Select Third-party apps with account access. Select Manage third-party apps.
Find Schoology and click on it. Select Remove access.
Click OK to confirm.
In Schoology, under Resources > Apps, you will notice the Drive is not connected.
Click on the Google Drive Resource App to reconnect it.
Check under one of the student's assignments to be sure the Drive is connected.
If that doesn't work, then follow additional steps for reconnecting the Google Drive Resource App in Schoology.